This invention relates to an apparatus for controlling an internal combustion engine operable on either of gasoline fuel, alcohol fuel and gasoline/alcohol fuel blend and, more particularly, to an apparatus for controlling the idling speed of such an engine.
For example, Japanese Utility Model Application No. 63-41015, filed by the same applicant of the invention, discloses an apparatus for controlling the idling speed of an internal combustion engine operable on gasoline fuel or gasoline/alcohol fuel blend. The control apparatus sets the engine idling speed at a target value calculated as a function of engine coolant temperature. That is, the engine idling speed is set at a greater value as the engine coolant temperature decreases. In such an engine idling control apparatus, however, the target engine speed calculation is made regardless of the alcohol concentration contained in the fuel supplied to the engine. Because of this, the harmful emission of aldehyde from the engine will increase as the alcohol concentration contained in the fuel increases if the engine idling speed is set at a target value appropriate for gasoline fuel. The aldehyde concentration contained in the exhaust gases discharged from the engine is three or four times greater in the case of alcohol fuel than in the case of gasoline fuel. Although the catalytic converter can purify 90 or more percents of aldehyde emission when fully activated, a great amount of aldehyde will be discharged to the atmosphere until the catalytic converter is activated. In addition, any attempt to reduce the harmful emission of aldehyde by setting the engine idling speed at a target value appropriate for alcohol fuel will result in substantially poor fuel economy.